mbuf: add help about Tx checksum flags

Describe how to use hardware checksum API.

Signed-off-by: Olivier Matz <olivier.matz@6wind.com>
Acked-by: Bruce Richardson <bruce.richardson@intel.com>

diff --git a/lib/librte_mbuf/rte_mbuf.h b/lib/librte_mbuf/rte_mbuf.h
index faa9924..1739e37 100644 (file)
--- a/lib/librte_mbuf/rte_mbuf.h
+++ b/lib/librte_mbuf/rte_mbuf.h
@@ -100,12 +100,16 @@ extern "C" {
 /* add new TX flags here */
 #define PKT_TX_VXLAN_CKSUM   (1ULL << 50) /**< TX checksum of VXLAN computed by NIC */
 #define PKT_TX_IEEE1588_TMST (1ULL << 51) /**< TX IEEE1588 packet to timestamp. */
-/*
- * Bits 52+53 used for L4 packet type with checksum enabled.
- *     00: Reserved
- *     01: TCP checksum
- *     10: SCTP checksum
- *     11: UDP checksum
+
+/**
+ * Bits 52+53 used for L4 packet type with checksum enabled: 00: Reserved,
+ * 01: TCP checksum, 10: SCTP checksum, 11: UDP checksum. To use hardware
+ * L4 checksum offload, the user needs to:
+ *  - fill l2_len and l3_len in mbuf
+ *  - set the flags PKT_TX_TCP_CKSUM, PKT_TX_SCTP_CKSUM or PKT_TX_UDP_CKSUM
+ *  - set the flag PKT_TX_IPV4 or PKT_TX_IPV6
+ *  - calculate the pseudo header checksum and set it in the L4 header (only
+ *    for TCP or UDP). For SCTP, set the crc field to 0.
  */
 #define PKT_TX_L4_NO_CKSUM   (0ULL << 52) /**< Disable L4 cksum of TX pkt. */
 #define PKT_TX_TCP_CKSUM     (1ULL << 52) /**< TCP cksum of TX pkt. computed by NIC. */
@@ -115,8 +119,12 @@ extern "C" {
 
 #define PKT_TX_IP_CKSUM      (1ULL << 54) /**< IP cksum of TX pkt. computed by NIC. */
 #define PKT_TX_IPV4_CSUM     PKT_TX_IP_CKSUM /**< Alias of PKT_TX_IP_CKSUM. */
-#define PKT_TX_IPV4          PKT_RX_IPV4_HDR /**< IPv4 with no IP checksum offload. */
-#define PKT_TX_IPV6          PKT_RX_IPV6_HDR /**< IPv6 packet */
+
+/** Tell the NIC it's an IPv4 packet. Required for L4 checksum offload. */
+#define PKT_TX_IPV4          PKT_RX_IPV4_HDR
+
+/** Tell the NIC it's an IPv6 packet. Required for L4 checksum offload. */
+#define PKT_TX_IPV6          PKT_RX_IPV6_HDR
 
 #define PKT_TX_VLAN_PKT      (1ULL << 55) /**< TX packet is a 802.1q VLAN packet. */